The present invention relates to polycarbonate compositions comprising blends of polycarbonate resins and acrylonitrile-butadiene-styrene terpolymer.
Polycarbonates are well known, commercially resinous materials having a variety of applications. Such polycarbonates may be prepared by reacting a dihydric compound, such as 2,2-bis(hydroxy phenyl) propane with a carbonate precursor such as phosgene, in the presence of an acid bonding agent such as sodium hydroxide. The resins are tough, rigid, have high softening temperatures, good impact strength, are usable over wide temperature limits, exhibit good dimensional stability and creep resistance.
Blends comprising polycarbonate resins and acrylonitrile-butadiene-styrene resins are known. For example, Yonemitsu U.S. Pat. No. 3,896,185 discloses molding compositions comprising polycarbonate resins and a rubber-modified chlorinated styrene resin. The chlorinated styrene resin can be a terpolymer of chlorinated styrene, butadiene and acrylonitrile. The blend is said to possess excellent mechanical properties, moldability, impact strength and flame resistance. Holub et al U.S. Pat. No. 4,226,950 discloses thermoplastic molding compositions comprising polycarbonates, an alcohol terminated polyester of neopentyl glycol and adipic acid in admixiture with an olefin rubber and a component which can be an acrylonitrile-butadienestyrene resin. The blends are said to have an improved processability and improved impact strength. Dean U.S. Pat. No. 4,491,647 discloses a blend comprising a polycarbonate, a rubber-modified methacrylate resin and an acrylonitrile-butadiene-styrene resin. The blends are said to have a higher degree of compatibility. Sakano et al U.S. Pat. No. 4,490,506 discloses thermoplastic compositions comprising a polycarbonate resin in combination with an acrylonitrile-butadiene-styrene resin having an improved moldability and impact resistance. Sakano U.S. Pat. No. 4,317,891 discloses molding compositions comprising polycarbonate, acrylonitrile-butadiene-styrene, and a polyamide resin composition having improved solid resistance, paintability and moldability.
One problem with such high impact strength polycarbonate blends is that their impact properties deteriorate rapidly at low temperatures, e.g., -20.degree. C. The addition of styrene acrylonitrile graft polycarbonate to ABS and polycarbonate blends have been shown to improve low temperature toughness. Unfortunately, styrene acrylonitrile graft polycarbonates are quite costly to produce.